Studies have been performed to determine whether variations exist between surface membrane glycoproteins of hind limb cells from normal mouse embryos and those which carry the skeletal mutation, brachypodism. Cells were labeled with I125 and the glycoproteins were analyzed by SDS-acrylamide gel electrophoresis. At the 11-day stage normal cells contain glycoproteins of 55,000 and 27,250 molecular weights. By 12 days of gestation four major glycoproteins are present with molecular weights of 55,000, 43,000, 36,000 and 27,250. Cells from 13-day hind limbs contain five glycoproteins with molecular weights of 55,000, 36,000, 20,750, 27,250, and 18,300. Brachypod cells from the same embryonic stages contain 55,000, 43,000, 20,000,and 16,000 molecular weight glycoproteins at 11-day stage; 27,250, 20,000, and 16,000 molecular weight glycoproteins at 12-day stage; and 29,750, 27,250, and 18,300 molecular weight glycoproteins at 13-day stage. In all cases the glycoproteins from mutant cells had lower radioactivity than normal. In another series of experiments 11-,12, and 13-day normal hind limb cells were formalin fixed, washed, and added to 12-day normal limb mesodermal cultures to observe any effect on chondrogenesis. Eleven-day cells depressed hyaluronic acid and enhanced chondrogenesis by removing a hyaluronidase inhibitor. No effect was observed with 12- or 13-days cells.